Alright. Here comes a special for our friend who's stuck in level 3. :)

[Let's see. Level 1... finished, level 2... finished, level 3... finished.]

Ok, the problem seems to be the red opponent. He has a nice amount of
people and goods, he replaces lost labs quickly and builds very dense.
A conservative approach took me 26 years. I conquered the red's lab and had
my wizard tear it down. One enemy lab less and some resources for free.
Then I had to look for the other opponent. First, I conquered the tower,
had my wizard tear it down... and the way was more or less open. Same
procedure for his lab. Meanwhile, our red colleague has two new
laboratories. Grmpf. And now we're running into trouble. This guy's
buildings stand so close to another that you cannot access any of them
without defenders rushing out of the neighbor buildings. If this is your
major obstacle, there is a cure. :) But some general help first.

- In order to get the necessary army ASAP, you need to generate lots of
  offspring. The ideal place is the peasant's hut but one of them won't get
  you too far. Since you normally have more maidens than you'd ever need,
  you should build two peasant's huts and fill them with 6 maidens and 3
  peasants each. (You know that the male:female ratio affects the
  preferred gender of the offspring, don't you?) That ensures that you have
  enough workers as well as a nice reproduction. And it makes the guys in
  the peasant's huts damn happy. ;)

- If you want to approach a building, avoid passing other buildings too
  close. You will have enough to do with the defenders of your target.
  There is no need to attract the attention of third parties.

- The same is true when you are passing enemy #1's territory to get to
  enemy #2. Don't call your troops over long distances. The pathfinding
  routine might take them to a sightseeing trip through an enemy city
  center. (Hi Paul! :) ) Call them to a point on the way, wait until they
  arrive, then proceed to the next waypoint and finally to the target.
  Control is everything.

- Avoid erecting buildings you don't need. It is nice to have four
  laboratories, a brewery, a fishery, sure. But they bind workers you
  need elsewhere. One farm, one water source, that should be enough for
  level 3. Although I had to exchange some spare goods for food from time
  to time.

- If potentially dangerous buildings (barracks, towers) are in your way,
  consider an attack. And to make a counter attack impossible without the
  need of keeping guards and/or knights inside, have a wizard ready, send
  the inheritants back to the HQ and tear it down. No, not the HQ. :) This
  is even more attractive now that we get some resources back when we scrap
  a building.

And here comes the promised secret master plan for level 3:

a) You know where the red enemy resides.
b) Now that your population rises faster than those of your opponents,
   you can have loads of soldiers in a very short time.
c) He doesn't have that many soldiers in early stages of the game.
d) Forget the task! Take some troops and invade the red enemy's HQ!

His lab is lost, he will never build another one, and you can relax and
care about the yelloy enemy. The whole level is possible in less than 20
years. :-O

HTH.